This invention relates to an attachment for preventing coronal discharge in high voltage insulators. In greater particularity the invention relates to a coronal ring with an improved positive clamping means which allows for mounting the ring to a polymer insulator end fitting. In even greater particularity, the positive clamping means utilizes two keeping elements with secured fasteners for ease of installation especially in hot line situations.
Corona is a discharge caused by electrical overstress in insulating materials. The occurrence of corona is often associated with the electrical failure of the insulator or insulating materials. In solids the occurrence of corona can result in the deterioration of the insulating material.
In high voltage transmission lines, the insulating material in which coronal discharge occurs is the air surrounding the conductor or insulators of the transmission line hardware. Thus, in the context of transmission lines, corona has been described by the American Standards Association as: a luminous discharge due to ionization of the air surrounding a conductor around which exists a voltage gradient exceeding a certain critical value. These discharges occur as the electrons from the intense electric field surrounding the conductor exceed a critical value. Normally, the electrons collide with air molecules such as oxygen or nitrogen and the electron bounces off with no transfer of energy to it. However, when the intensity of the electron exceeds a critical value the velocity of the electron is such that its collision with the air molecules is inelastic. Thus, an electron is knocked from an outer shell of the air molecules ionizing these molecules. The molecule with the missing ion is now a positive ion. The positive ions, e.g. nitrogen ions, are attracted toward the negative conductor in a sluggish manner due to their large size. These ions manage to capture free electrons which results in a quanta of energy being released as the energy level of a neutral molecule is less than that of the positive ion. The energy is radiated as an electromagnetic wave in the visible light range from the recombining of nitrogen ions with free electrons.
The coronal discharges result in deterioration of synthetic materials comprising insulators on transmission lines. The discharges also result in the loss of efficiency in transmitting current along such hardware and radio disturbances or interference caused such discharges. Increased expenses in the form of replacement insulators and related labor are also a result of coronal discharge.
In the past, numerous shielding and ring devices have been disclosed which spread and deconcentrate the electric field surrounding conductors and insulators to prevent coronal discharge. The majority of the control devices use some type of transverse mounting means such as a suspension clamp or a yoke plate connected to a suspension clamp to hold the control devices in place. These mounting means are complex to manipulate and utilize numerous pieces such as fasteners and U-shaped clamps. The manipulation of complicated mounting means makes installing and removing the control devices difficult for the line worker. Line workers are in a precarious work environment high in the air where the manipulation of mounting means increases the length of time it takes to complete a job. Should one of the pieces become completely disengaged and fall to the ground, the line worker must have a replacement piece handy or retrieve the missing piece from the ground in order to complete the job. Occasions may arise wherein the control devices must be installed or removed in a hot line situation and the added manipulation of the mounting means increases the risk of injury to the line worker.
One apparatus designed to simplify the mounting procedures was disclosed in U.S. Pat. No. 5,552,566. In the ""566 patent, the mounting apparatus consisted of a single clamp mounted superjacent the integral clamp assembly of the corona ring. Operation of the single clamp involved one captive fastener extending through the integral clamp and the single clamp to secure the insulator end and the corona ring into appropriate positions. However, since development of that apparatus, the standard issue insulator has been redesigned, and the single mount apparatus disclosed in the ""566 patent is not readily adaptable to the new insulator design. The new insulator design as disclosed in U.S. Pat. No. 5,877,453 was developed for use in extremely contaminated environments. The ""453 insulator design does not fit securely into the ""566 corona ring clamping means and as a result additional manipulations are required by the line workers in order to securely attach the insulator to the corona ring. As a result, there is a need in the transmission line hardware industry for an improved mounting apparatus for simple installation and removal of a corona control device or ring for use with the newer composite insulators.
It is an object of this invention to provide an improved apparatus for preventing coronal discharge in high voltage transmission insulators in which two pivotally mounted keeper mechanisms rotate simultaneously from an insulator receiving position to an insulator secured position to secure the insulator against the corona ring and in which the keeper mechanisms are secured by captive fasteners to provide for ease in installation and removal in hot line situations.